In a normal heart, the sinoatrial node, the heart's predominant natural pacemaker, generates electrical impulses, called action potentials, that propagate through an electrical conduction system to the atria and then to the ventricles of the heart to excite the myocardial tissues. The atria and ventricles contract in the normal atrio-ventricular sequence and synchrony to result in efficient blood-pumping functions indicated by a normal hemodynamic performance. These intrinsic action potentials can be sensed on a surface electrocardiogram (i.e., a “surface ECG signal”) obtained from electrodes placed on the patient's skin, or from electrodes implanted within the patient's body (i.e., an “electrogram signal”). The surface ECG and electrogram waveforms, for example, include artifacts associated with atrial depolarizations (“P-waves”) and those associated with ventricular depolarizations (“QRS complexes”).
When people have irregular cardiac rhythms, referred to as cardiac arrhythmias, or poor spatial coordination of heart contractions, diminished blood circulation may result. For such persons, cardiac rhythm management (CRM) systems may be used to improve these conditions. CRM systems include, among other things, pacemakers which deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart. By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, improving efficiency. Another type of CRM system includes defibrillators that are capable of delivering higher energy electrical stimuli to the heart. Such defibrillators include cardioverters, which synchronize the delivery of such stimuli to sensed intrinsic heart activity signals. Defibrillators are often used to treat patients with tachyarrhythmias, which can be thought of as abnormal heart rhythms characterized by a rapid heart rate. Fibrillation is a form of tachyarrhythmia further characterized by an irregular heart rhythm.
Upon implantation, a CRM device is programmed to perform in response to detected electrical or mechanical disturbances within the heart. How the device is programmed may have a direct impact upon patient outcome. When the device is first implanted, a caregiver may rely upon historical data to determine how to set the programming parameters to be used until the next follow-up appointment, during which time results may be measured and recorded. After a specified period of time, the patient returns for a follow-up visit with the caregiver, the results are evaluated, and the device is re-programmed, if appropriate.